This invention relates to the field of catalytic fuel reforming, and provides a catalyst support capable of operation at high temperatures, such as are encountered in a steam reforming process.
A fuel cell produces an electric current using hydrogen as a starting material. The hydrogen required by a fuel cell is typically made by a steam reforming process, in which a hydrocarbon fuel is reacted with water, the water being in the form of steam. The steam reforming reaction is endothermic, and therefore requires a source of heat.
Other industrial processes, such as oil and gas refining, ammonia and fertilizer production, hydrogenation of oils and chemicals, and iron ore reduction, also use hydrogen as a beginning or intermediate part of the process. Most of these processes also use steam reforming of hydrocarbon fuel, usually natural gas, to make the hydrogen.
In the prior art, it has been known to use shaped ceramic catalysts in packed beds to support the steam reforming reaction. These packed beds are typically arranged in tubes that are about 4-6 inches in diameter, and up to about 40 feet tall. Many such tubes are arranged in a furnace to supply heat for the reforming reaction. A typical furnace temperature is about 850° C. Steam and natural gas enter the top of the tubes. A catalytic reaction takes place through the vertical packed bed, producing hydrogen, among other products such as carbon monoxide and carbon dioxide, which exit from the bottom of the tube.
The above-described packed-bed system has two major disadvantages. First, heat transfer from the tube wall into the packed bed is a limiting factor. While heat can be quickly transferred, by conduction, through the metal tube wall, it is difficult to transfer heat through the packed media so as to reach the media near the center of the tube. Consequently, most of the system performance comes from the packing near the walls, and the packing near the center is only marginally effective.
Secondly, the thermal expansion mismatch between metal and ceramic limits the durability of the system. On furnace startup, the tubes expand, but the ceramic packing does not. As the tube expands, the ceramic settles to fill the void created. When the furnace is later shut down, the tube contracts and crushes the settled ceramic media, forming a powder. Several heating and cooling cycles can produce enough cracked material to block the reactor, at least partially. Consequently, the media must be changed, typically every 5-7 years. Changing the packed media is an expensive process, and requires that the reactor be shut down for a period of time.
The present invention solves the above-described problems, by providing a catalyst support that more effectively moves heat from the outer wall of a metal tube to the center region of the tube, and back. The catalyst support of the present invention also avoids the thermal mismatch problem that plagues packed-bed catalyst systems, and thus avoids the crushing of ceramic material that leads to eventual replacement of the media. The support made according to the present invention can be expected to last for the life of the plant.